A product that tests for traces of alcohol in breast milk has triggered warnings that mothers who rely on its findings could damage the health of babies and encourage binge drinking.

Milkscreen, which goes on sale in Britain this week, contains test pads that change colour on contact with breast milk containing alcohol, warning women that it is unsafe to breastfeed.

Experts, however, say that there is no clear answer to how much a new mother can drink before the alcohol gets into her milk, nor how long she should wait after drinking the alcohol to ensure it is not passed on to her baby.

The British Medical Association advises breastfeeding women not to drink at all; the Royal College of Obstetricians and Gynaecologists says one or two units a couple of times a week is "probably" safe. Old wives' tales, however, advocate moderate drinking while breastfeeding, claiming porter can give new mothers extra energy, beer can increase milk production and alcohol in general helps infants sleep.

But, according to Milkscreen, infants can safely consume breast milk with an alcohol concentration of approximately 0.03%. The threshold is, admits Julie Jumonville, founder and chief product officer of the UpSpring baby care project company, based on a number of research papers published by the American Academy of Paediatrics that look only at the impact of alcohol in breast milk on babies' sleeping and feeding patterns.

"There is other research showing that any alcohol at all in breast milk can impair the motor development skills of babies, but the majority of research focuses on the impact on sleeping and eating, and cites this 0.03 percentage, so that is what we have concentrated on," said Kimberly Schram of UpSpring.

"We are not marketing this product at problem drinkers: we aim to appeal to responsible mothers."

An alert is triggered by a concentration of alcohol in the breast milk greater than 0.02%. "There is no way to convert that alcohol percentage into a number of drinks," said Jumonville. "It is dependent on so many factors, including body weight, the type of alcohol consumed, and food intake."

Some studies suggest that about 2% of the alcohol a mother consumes will enter her bloodstream, and therefore her milk, with levels continuing to rise in milk for between 30 and 90 minutes after the last alcoholic drink. Other research says that a newborn's immature liver makes it very difficult to process even small amounts of alcohol.

There is very little research on the impact of alcohol on breastfeeding, but Schram is adamant that Milkscreen is both safe and accurate. "We are in the process of finalising approval with the US Food and Drug Administration, so we are not able to share accuracy rates at this time," she said. "However, from the clinical studies that have been performed to date, we are confident in the accuracy of our product and the peace of mind that it provides to breastfeeding women."

Patrick O'Brien, a spokesman for the Royal College of Obstetricians and Gynaecologists, questioned the validity of the research on which Milkscreen is based. "It is worth noting that the current evidence is not robust enough to exclude any risk from low-to-moderate levels of alcohol consumption," he said. Professor Sir Charles George, chairman of the 2007 foetal alcohol spectrum disorders report by the board of science of the British Medical Association, agreed. "There is considerable debate as to the adverse effects of maternal alcohol consumption at low-to-moderate levels of drinking," he said.

Others are concerned the test could damage babies' health and encourage binge drinking. "It's risky to apply any blanket measure to the issue of alcohol and pregnancy," said Susan Fleisher, founder of the National Organisation for Foetal Alcohol Syndrome-UK.

"There are lots of reasons why this test could be dangerous: alcohol might only stay in a woman's system for 12 hours, but it can stay in a baby's system for up to 72. This means there is a real danger of babies accumulating alcohol in their body."

Dr Joan Younger Meek, editor of the New Mother's Guide to Breastfeeding, believes there can be no responsible drinking while nursing. "We do not have enough information to say exactly how much is all right," she said. "We worry about the effects of alcohol on the baby's developing brain and we do believe that consumption of alcohol by the feeding mother can cause problems with the baby's motor development."